How important this is depends a lot on what you cook. The more smoke you generate, the better hood you need.

Not all hoods suck air up uniformly within their catchment areas, and not all hobs are used to cook stuff that smokes. You want to center the strongest suction area within your hood above the hob that needs the most suction.

That said, I'd go for the larger cfm fan; 600 cfm might be better still. And I'd aim for close to 30" height. The higher up the hood is, the more smoke is apt to be lost (especially with a relatively low powered fan).

It may be difficult to find an optimal hood height for both you and your wife, given your height difference. Make a mock-up of the perimeter of your hood out of a strip of cardboard, and tape it up to the wall at various heights, to see what seems best for each of you. That can help you understand where the trade-offs are.

Since smoke/effluent rises up and outward like a cone, one consideration is how far your 24" deep hood extends toward you, in relation to the cooktop's hobs (esp. the largest, or whichever one will generate the most smoke). Watch out if its snug against the back wall and you're grilling on a large front hob; smoke escapes more easily that way. This may be more a problem for you.

Finally, there are hoods that can be raised or lowered slightly. They're expensive, and may only be for island installations, so these may not be a solution for you.

My Broan Elite 64000 wall hood (~600 cfm) is mounted about 27" above an E'lux induction range. Its adequate.

The 30" minimum height spec above the cooking surface (= the distance from the internal cooking surface of a thin frypan in normal operation to the bottom of the range hood) is a common building code requirement not a maker's recommendation.
The more powerful the range, the pickier that distance becomes.

DH is 5'11", and I am 5'3". We have an all-gas 30" range with a 30" wide hood, that is mounted about 30" above the top of the range. I find people's worries about hitting their heads on hoods to be overblown. Your brain gets quickly accustomed to where the hood is located, and you don't have to think about it. You may hit your head once or twice when first installed--if even that--but no more.

You don't want to spend all that money on a hood, and then hang it so high that it is not effective at capturing the smoke and grease before it can escape to the rest of the house. What would be the point of spending that money then?

As to the hood liner being visible - that, as you said, is not a factor worth considering. It's a hood, and it's in a kitchen, so you expect to see it. I would at least try to get a baffle filter hood, rather than one with mesh filters. Mesh filters will clog with grease, maybe even after one night of hamburgers, and you will be able to see that. A lot of people actually like to see the liner, gives it a "kitchen-y" look.

One requirement is that combustibles not be too close to sources of fire, which can even be a pan on an induction hob. I believe this is the actual basis for the 30-inch minimum rule.

As for head hitting and sight lines, while you are accumulating the cardboard to build chac_mool's mock-up, my advice would be to sketch a side view of the configuration, to scale, and use stick figures to see if there will be bending interference at specific hood heights. You can check bended and erect sight lines into pans. You can check reach to pans to see whether you have to bend to lift a pan or stir the contents. A drawing will avoid spending time reconstructing the mock-up for different hood sizes and mounting heights.

Also consider whether you might need to remain in a position that is uncomfortable (excluding hood interior cleaning, which will always be uncomfortable), or if hood lamps will provide an undesired warming function on one's head, etc.

In conclusion, please note that higher hoods require larger apertures to collect the rising and expanding effluent. Higher flow rate is needed only in proportion to the increased aperture area, and not to "suck up" the effluent from farther away (because that is not how hoods work).

kas

Lots of good advice here, I've nothing to add. Except to agree with the overconcern about height-positioning. If you search on this topic you will find there have been many such threads in the past. I was worried about this issue too and - with trepidation - decided to trust the consensus that it wasn't likely to be a problem and I haven't had any reason to regret that "faith". I'm 5-8 (And shrinking), dh is 6-0 and the recommended height of 30" up (from 37" counters) has not been a problem. Remember this ergonomically -- when you bend forward to get underneath a hood, the upper part of your body goes on an angle, so your height is diminished from its full standing height. If you need to get underneath your hood, you'll be bending forward to reach back burners, at least that's so in my case. At that point, I'm way less than 5-8 for sure!

And I hear the periodic cries to reason about how smaller than larger hoods can be good and good-enough and the world won't come to an end if you don't put a 50" x 30" covering over your 32" range. However, I've looked at those smoke plumes now and do see the wisdom of "bigger is better". It's hard to capture all you'd like to capture and every little extra inch helps. That's the operative word - helps. There are tradeoffs with cost and design and the rest of it all. But in general, I have to say you'll appreciate what extra size and planning you put into all of this. IMO, particularly in terms of the depth. I have a 27" deep hood and I occasionally regret it's not deeper. How things work with a 24" hood I can only imagine but it seems to me it would be not-good...

IMHO anything at all that kas has to say is advice worth heeding; it is invaluable.

Thanks to all of you...good information.

Since I posted, my wife and I mocked up a cardboard hood and mounted it at different heights above the cook top: 30", 32", 34", etc. We decided 30" was a good compromise for our heights of 6' and 5'4". At 66" above the floor, the bottom of the hood came to just below my eye height and about 6" above her eye height. Any higher just seemed to be too high for her, since the light and fan controls will be on the underside of the liner. I may have to bend over a bit to see the controls but she won't have to reach up so high. Also, that height (versus higher) will give a better capture and provide a more aesthetically pleasing width/height profile (36" W x 24" D x 30" H) with a 20" or so chimney width (including the crown molding).

I've discounted the "head bumping" issue for me because, as many posters have mentioned, I'll get used to it. As for the controls, I'll also soon learn where they are and be able to intuitively reach right to them.

Thanks to you all.